Apparatus for electrochemical machining

ABSTRACT

Apparatus for electrochemical machining of metals utilizing a highly conductive electrolyte wherein a self-contained electrolyte circulating system is provided for each machine or pair of machines, and electrical isolation is maintained between this self-contained electrolyte circulating system and the main supply system during the machining operation to prevent electrical interaction between a substantial number of machines which are supplied from the same source of electrolyte.

United States Patent Tyler et al. p

APPARATUS FOR ELECTROCHEMICAL MACHINING Roger K. Tyler, Redford; JackNew, Garden City, both of Mich.

TRW Inc., Cleveland, Ohio Apr.'l3, 1972 [75] Inventors:

Assignee:

Filed:

Appl. No.:

(1.8. Cl. 204/224 M, 204/l29.7

Int. Cl 1323p 1/00, 823p 1/04 Field of Search 204/224 M, 129.7

References Cited UNITED STATES PATENTS 8/1968 Mikoshiba et al. 204/l29.71/1972 Williams 204/224 M [1 1] 3,755,127 [4 1' Aug. 28, 1973 4/1972Fulkerson et al. 204/224 M 6/1972 Fleury et al. 204/224 M PrimaryExaminer-John H. Mack Assistant Examiner-D. R. Valentine Attorney-Benjamin H. Sherman, J. Arthur Gross and James Van S anten et a1.

[57] ABSTRACT Apparatus for electrochemical machining of metalsutilizing a highly conductive electrolyte wherein a selfcontainedelectrolyte circulating system is provided for each machine or pair ofmachines, and electrical isolation is maintained between thisself-contained electrolyte circulating system and the main supply systemduring the machining operation to prevent electrical interaction betweena substantial number of machines which are supplied from the same sourceof electrolyte.

5 Claims, 1 Drawing Figure AIK 39 v V 4 33-4 J J2 v r ABPARA'EUS: EGRiEEEQ'IERQEHEM-llkh wcmmuo;

QKGRQUND; on INV-ENEIEIGN? 2 lutionncauses localorint'ermittentpassivityofthewo'rk which makes machining; difficult.

The rate of flow ofi the' electrolyte" is im'po'rtant be; I

causethe electrolyte: must remove the lie'atancl the 5, products ofthe'chemical reactionz Generally' the larger the ratio of" flow to:current, v the: better the: removalot heat and reaction products.However; the cost ofpumpih'g' increases asl thex flow increases, and:excessive: fl'owv rate: can: cause. cavitation effects an'd nonuniformbenofg such.: machines; is; individualized} andi electrically;metalremoval;-

separated; from, the main; storage; tanks; during; the electrochemicalmachiningoperation;.

2 1;)eseriptionofef'the; Brion Afli E ctrochem cali mac nimy,vusuallyreferred? to as. ECM'? is, the; controlled removal 0 metali by; anodic;dissolution in ans electrolytic: cell; in; which; the WOflh piece theanodeandgthedooliis the-cathode; 'I3he:elec:- trolyteispumped{throughrawgapibeteweemtheioolandi the; workpiece While direct?current: is; passedi through; the; cell? at, a; low. voltageto,dissolve; metal? from the; workpiece at approximately.- 1OOjzpercentaeffiCiencv.

Electrochemical smachittine;cambe:v used; to l do. work: hat: Quld-z e it'ficultm ntp ssihlexhymneshaniealima, ling, h s. work: ncludes-rmachining; r i metals: uch as l ardened teel; andi. heat: resisting;alloys; and odd-shaped small; deep? holest-, Electrochemical; ma, hiningals sed ong rations-lsuehwaefacemilling; dehurring'tet h ng andimarkinhil :man i rentgt s'-, ,fii'a eous-soluti saofz on 301 owertsupplyhas-sitsposit1ve -side= connectedto' the": workpiece: andzi itsnegative? side: to th'einozzle; Inlet means are= provided" at? the:nozzle: for" introducing; a:

gan c, 9mn unstehave bemused astelectroiy es, amwigheim0stQcQmmQItatercpncentratedjsolutionsaoff ulfuric; ac d; ydrochloric acid? onsolutionstofsa al siat. hese; trong asidt lutionsfretaimtheranodicauyremovedim talun solutmn'land:domotzgmducezsludger 351;;electrolyteyhasmanicipamd in,mwelectmchbmicalima; chiningg; operation;thestorage: tank having; fi'lteringg me-ansiorother; means-foriremovinggrany contaminants present:v Therused electrolytefifromall oftheimachiningg' stations is suppliedito. th'errelatively la'rgezcapacitystor "age: tank b'ut eachwmillingrstatiom wh'ichumayinclude ones-'orstwo-machinesz has-its self-contained:elctrolvte.i circulating system; Thesystem includes a 1 relativelysmall capacity; tank 'arranged tobevfeda'fromathe large:

N capacityv storage": tank; when" no machining;vv istakin'g: 5 place; At:least '-one:.container is imm'ersedz'iin therrela tivelyy;vv smalltank; and fluid; pressure means'flsuch as n er h r on instofimachiningfi helsuc ess ofith -;.cl ctrochemical.machinjng operafitiqlt'is to. aiarge extentdependentaupomthepropericon: "O110fz heo ariabpresentt Thesmostzimportant -:vari-. I blessaleable-1 01 ssttqlytea. opos tions s spended-i solids: conte n. temperature, and flom rates;theiconstruction; and: finishh of ithe to olgand; fixture material;thezworkpiecesmaterial andjtscmdition, andthe cutting g apl Foraccuratema chi ling; fi teady;statetcondit enrshouldsbeestablished; 4in.twhisihzthe dissolutionslo the workpieceamateriallis g y-rthe; feedpfA e-4001.: This.trequiressasunim; control abletoolr e d ter;

Qu r ntxdens tys sltheechief facton imdet rmining th' p rm ssi i atczotoothed: cess isgoye rned bly FaradayEslLawr Other sfa'ctors re? mainingcon stant," the rate ofipenetration-varies directly 5 with thect fltentgCurrent adensity also affects that-surf The; lectrolyte in; theelectrochemicali machining; process has-.three functions, thatoilcartyigahe' urrent micatandre ectrochem ca stab y dtflnabsence; of -passiv inseftect ;i

Conduct-wit f the electrolyte-sjs important because it afl'eetspowerrequirements andrate ;.of penetration An over eencentrated solution {may:,become,;saturated.-;

and r allowflthe L' -formation of crystals =that 1C3]! --dam age;

' pumps-waives instrurnents,qandvgpipes. tA:.very weak ',so.,,-

di ateqthe urrent sdensity ,the 40 must ghfajw i highselectrical;-7conduct ivity',.' lows. toxicity The control of these: interrelated:variables: isquite difficult? on: a production) line: basis; it Becomesmore difficult. whem a: single: storage tank is used t'osupplyelecltrolyte: to a; large number of machining, stations:

15:? sincerthe' electrolytetissuch agood' co'n'ductor 'tliat elec tricalinterference:v cam exist Between: the variousma+ chiming; assemblies.on. a: production" line" through: the mediumoftlie-x'storagatanl'usedltosuppiynhe electrm' lyte'. .sinceecurrentdensity, and' voltagearecritical items 20; in'-- aproperz'electrochemical i machining; operation; this The: present?invention: prov-ides am electrochemical machining; apparatusi assembly;ir'icludinga at; least-l one:

electrochemical machining: stations including i a s nozzle and: afworkpiccear to: bermachined Ai direct currenthighlyaconductive:electrolytezthereins A =relativeljr -large capacitygsmrageantanlc receives" the. electrolyte. after thecompressed air isemployed forremptyingrgtheielectro= lytetcontainedvinrthe; containerandsideliveringgit no a :1 particular machining stationaInteraction:betweenethe 'fifi P machining station andsthe: largecapacity-storage tanki is prevented; by providing ahvalve 'meanscontrolled' bythe power supply of. the system to :interrupt theffliiidcommunication: between: the :relatively; largecapacity tankandc,thel'relatively small capacity tank when the "power.supplyisenergized:

BRIEF-F-DESCRIPTION' OPE-THEE DEA-WING} Other .objects features andadvantages of the-zinvention ::will be readily apparent from-1' the"following .de-

scriptonzof 1a.zpreferredcembodiment thereofl taken in" conjunction withthe accompanying drawing; althouglr variations and. modifications may beefl'ected.'without departing {from the spirit. andv scope of r thecnovel con-I cepts of the disclosure; and in which: 7

lines are used to indicate fluid conduits, while single lines are usedfor the electrical wiring.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the FIGURE, referencenumeral indicates generally an electrochemical machining stationemploying a machining tool 11 under the control of a constant tool feeddevice generally indicated at reference numeral 12 of the drawings. Thetool 1 1 includes a nozzle 13 whose dimensions are exaggerated for thepurposes of illustration. The tool 11 is connected to the negative sideof a DC. power supply 14 by means of a lead 15. A workpiece l6constitutes the anode of the electrochemical machining system and isconnected to the positive side of the power supply 14 by means of anelectrical lead 17.

Used electrolyte collected from the machining station, and others likeit, is introduced via a conduit 18 into a large capacity storage andfilter unit generally designated at reference numeral 19 of thedrawings. The capacity of the unit 19 is sufficiently large to holdenough electrolyte to supply all of the individual machining stations.

The clarified electrolyte is pumped from the storage unit 19 to theindividual machining stations by means of a series of pumps, one ofwhich is illustrated at reference numeral 20 of the drawing. The outputof the pump 20 is under the control of a valve 21 which is operated by asolenoid 22 connected to a low voltage, low current portion of the powersupply 14 by means of leads 23 and 24.

The electrolyte from the storage unit 19 is pumped through a conduit 25into an electrolyte circulating unit generally indicated at referencenumeral 26 of the drawing. The electrolyte circulating unit 26 mayinclude a relatively small capacity tank 27 having a cover 28 thereon.The tank 27, the cover 28 and the various valves and fluid conduits areall composed of an inert or chemically resistant dielectric materialwhich may be a synthetic resin, glass, or a ceramic material.

Immersed within the electrolyte contained in the tank 27 is a pair ofcontainers 29 and 30 also composed of an inert, electrical insulatingmaterial. The containers 29 and 30 are provided with covers 31 and 32,respectively.

Electrolyte within the tank 27 is circulated by means of an impeller 33located within a housing 34 and driven by means of a motor 35. A conduit36 delivers the electrolyte sequentially to the containers 29 and 30,depending on which is on stream at the time. Air operated valves 37 and38 are provided for controlling introduction of the electrolyte into oneor the other of the containers. Each of the containers is also providedwith an overflow control valve 39 and 40, respectively, to directoverflow from the containers into their associated conduits 41 and 42,respectively.

Propulsion of the electrolyte is achieved through a pair of air pressurelines 43 and 44 under the control of air operated valves 45 and 46.Pressurizing of the interior of the containers 29 and 30 serves to forcethe electrolyte contained therein through a discharge conduit 47 or 48,under the control of air operated valves 49 and 50, respectively. Thevalves 49 and 50, when open, direct the electrolyte through conduits 51and 52, respectively, into a tool supply line 53 from which it isdirected into the interior of the tool ll through an inlet 54.

The operating conditions depend, of course, on the material beingmachined. Electrolyte temperatures are preferably maintained in therange from about to F. Pumping pressure on the electrolyte varies withthe inside diameter of the nozzle and generally ranges from about 10 to70 pounds per square inch with a range of 40 to 60 pounds per squareinch being preferred. Nozzle lengths may also vary appreciably, withlengths from 0.090 to 0.1 10 inch being useful for very small diameterdrilling. The inside diameter of the nozzle may vary considerably, witha range of 0.0003 to 0.001 inch being useful for very small holedrilling. The gap distance between the discharge end of the nozzle andthe workpiece may vary from about 0.030 to 0. l 50 inch in length withvan initial gap of 0.70 inch being preferred for efficient drainage ofelectrolyte.

The direct current potential between the anode and the cathode may rangefrom about 100 to 800 volts. This potential may be varied as themachining operation progresses, with an initial potential below 100volts being employed until dimples are formed in the surface of theworkpiece sufficient to direct jet streams away from the surface of theworkpiece. This voltage may then be increased incrementally as thecavities increase in depth. Starting currents as low as 0.10 to 0.30 ampere may be used until the cavity is sufficiently shaped to direct thejets away from the workpiece, whereupon the voltage may be increased tomaintain a current of about 0.75 to 1.5 amperes. The container 27 isfilled with electrolyte from the storage unit 19 at the end of the daysoperation, when the machining stations are shut down. Then, when themachining operations are to begin, the power supply 14 is energized,causing the solenoid 22 to close the valve 21 and electrically isolatethe large volume of highly conductive electrolyte in the storage unit 19from the individual machining units.

The various ajr operated valves on the containers 29 and 30 areprogrammed by means of a fluidic (air logic) sequential timing controlor the like so that continuous introduction of electrolyte is effectedinto the tool 11, with one container being filled as the other one isdischarging its contents. For example, assuming that container 29 isbeing filled and container 30 is delivering the electrolyte to the tool,valve 37 will be opened and valve 38 will be closed. Outlet valve 49will be closed and outlet valve 50 on container 30 will be open. Valve45 which controls the supply of compressed air will be closed, and valve46 will be open to provide the fluid pressure for discharging theelectrolyte through the discharge valve 50. The overflow valve 39 incontainer 29 will be open, and valve 40 will be closed. In the nextsucceeding cycle, when container 30 is being filled and container 29 isbeing emptied, the valves which had previously been open will now beclosed, and those which had been closed will now be open.

From the foregoing. it will be understood that the system of the presentinvention provides for individual control of electrolyte circulation forone or a few machining stations, while isolating each of the machiningstations from the main supply tank. In this way, close control of theelectrical variables at each station is rendered considerably easier tomaintain and electrical in teraction between the stations is avoided.

It will also be evident that various modifications can. be made to thedescribed embodiments without departing from the scope of the presentinvention.

We claim as our invention:

1. An apparatus for electrochemical machining comprising at least oneelectrochemical machining station including a nozzle and a workpiece tobe machined, a direct current power supply, means connecting thepositive side of said supply to said workpiece and the negative side ofsaid supply to said nozzle, inlet means at said nozzle for introducing ahighly conductive electrolyte therein, a relatively large capacitystorage tank receiving the electrolyte from said station afterparticipating in the electrochemical machining operation, a relativelysmall capacity tank in fluid communication with said relatively largecapacity tank, at least one container immersed in said relatively smallcapacity tank, fluid pressure means for emptying the electrolytecontained in said container, conduit means connecting said container tosaid inlet means at said nozzle, and

valve means controlled by said power supply to interrupt the fluidcommunication between said relatively large capacity tank and saidrelatively small capacity I tank when said power supply is energized.

2. The apparatus of claim 1 in which said relatively small capacity tankincludes a pair of said containers, and said fluid pressure meansoperates on each of said containers sequentially to provide a continuousstream of electrolyte into the inlets of said nozzles.

3. The apparatus of claim 1 which includes an agitating andpumping meansin said relatively small capacity tank.

4. The apparatus of claim I in which said valve means is an air operatedvalve.

5. The apparatus of claim 1 in which said fluid pres sure means includesmeans for introducing compressed air into saidcontainer for dischargingelectrolyte from the base of said container.

1. An apparatus for electrochemical machining comprising at least oneelectrochemical machining station including a nozzle and a workpiece tobe machined, a direct current power supply, means connecting thepositive side of said supply to said workpiece and the negative side ofsaid supply to said nozzle, inlet means at said nozzle for introducing ahighly conductive electrolyte therein, a relatively large capacitystorage tank receiving the electrolyte from said station afterparticipating in the electrochemical machining operation, a relativelysmall capacity tank in fluid communication with said relatively largecapacity tank, at least one container immersed in said relatively smallcapacity tank, fluid pressure means for emptying the electrolytecontained in said container, conduit means connecting said container tosaid inlet means at said nozzle, and valve means controlled by saidpower supply to interrupt the fluid communication between saidrelatively large capacity tank and said relatively small capacity tankwhen said power supply is energized.
 2. The apparatus of claim 1 inwhich said relatively small capacity tank includes a pair of saidcontainers, and said fluid pressure means operates on each of saidcontainers sequentially to provide a continuous stream of electrolyteinto the inletS of said nozzles.
 3. The apparatus of claim 1 whichincludes an agitating and pumping means in said relatively smallcapacity tank.
 4. The apparatus of claim 1 in which said valve means isan air operated valve.
 5. The apparatus of claim 1 in which said fluidpressure means includes means for introducing compressed air into saidcontainer for discharging electrolyte from the base of said container.